NORTHBROOK, IL, Aug. 27 -- Orders for rigid boards upticked in July and demand for flex circuits continues to be strong, according to the latest 90-day moving average of North American manufacturers.

For all board types, shipments rose 31.1% and bookings were up 42.2% vs. a year ago, said IPC, which administers the monthly poll. The figures may include some sales of products built offshore and brokered by the surveyed companies.

The July book-to-bill was 0.99 for rigid, up 0.04 points sequentially. The B2B for flex circuits remained even at 1.57.

The book-to-bill for all board types rose to 1.10, up 0.04 points sequentially.

The ratio is calculated by averaging the number of orders booked over the past three months and dividing by the average sales billed during the same period. A ratio of 1.06 means that for every $100 in shipments, $110 worth of PCBs were booked. An increasing ratio is generally considered a sign of a market poised to rise.

Shipments are up 34.8% year-to-date, bookings 43%. Combined July shipments fell 18.1% sequentially, while bookings inched up 1.9%.

July rigid shipments were up 17.6% and bookings 20.5% over last year. Year-to-date, rigid shipments are up 25.5% and bookings are up 23.1%. Among those surveyed, rigid shipments fell 21.2% sequentially and bookings dropped 7.5%.

July flex shipments were up 76.1% while bookings reversed last month's decline, rising 71.1% vs. last year. Year-to-date, flex shipments are up 77.8% and bookings 133.2%. Sequentially, flex shipments fell 3.7% and bookings were up 56.1%.

Flex sales, which include some value-added services, make up about 17% of total PCB sales in the IPC poll.

The data come from a sample of North American rigid and flexible PCB manufacturers.